1. Field of the Invention
The present invention generally relates to an apparatus and a method for coating small Nd—Fe—B magnets.
2. Description of the Prior Art
Such a method is disclosed in Chinese Patent CN100582290. The method includes a first step of shaping the plurality of Nd—Fe—B magnets including grease into a plurality of small Nd—Fe—B magnets. The next step of the method is cleaning the small Nd—Fe—B magnets. Next, the small Nd—Fe—B magnets are disposed in the compartment of the roller in the chamber of the furnace. Then the chamber of the furnace is sealed. After sealing the chamber of the furnace, air is removed from the chamber to reduce the pressure in the chamber to a first pressure range. The next step of the method is further removing air from the chamber to reduce the first pressure range to a final pressure range. At the final pressure range, an inert gas is fed into the chamber to increase the pressure in the chamber. Then, a film is deposited on the surface of the small Nd—Fe—B magnets.
Such an apparatus is disclosed in the Korean Patent Application KR20040052533. The apparatus includes a furnace including a side wall disposed annularly about a center axis and extending between a first end and a second end. A rear wall is affixed to the second end of the side wall defining a chamber between the side wall and the rear wall. A shaft is rotatably attached to the furnace and extending through the rear wall and into the chamber. A roller of permeable material is disposed in the chamber and attached to the shaft and having an interior surface defining a compartment for receiving the plurality of small Nd—Fe—B magnets. A plurality of target source holders includes at least one first target source holder and at least one second target source holder. The first target source holder is disposed on the side wall of the furnace defining a first exterior surface facing the roller for receiving a first target source and ionizing the first target source to provide a coating for the plurality of small Nd—Fe—B magnets. The second target source holder is disposed on the side wall of the furnace spaced from the first target source and defining a second exterior surface facing the roller for receiving a second target source to provide the coating for the plurality of small Nd—Fe—B magnets.
Due to the potential difference between the Nd-rich phase and the Nd2Fe14B phase, and an Nd—Fe—B magnet's hydrogen absorption properties, it is very easy for the Nd—Fe—B magnet to corrode. To prevent the Nd—Fe—B magnet from corroding, it is known in the art to provide an anti-corrosive coating layer on the surface of the Nd—Fe—B magnet. The common methods of preparing a film of anti-corrosion coatings on the surface of the Nd—Fe—B magnet include electrophoresis, spraying, vacuum coating, and electroplating.
For small Nd—Fe—B magnets, it is difficult to quickly fixate the small Nd—Fe—B magnets onto a common fixture. Accordingly, methods such as barrel plating or roll spray coating are used to provide an anti-corrosive coating on surface of the small Nd—Fe—B magnets. However, the presence of acid and base during the electroplating process can damage the small Nd—Fe—B magnets. The chemicals used during the spraying process can cause harm to the human body and the environment.
Presently, on some particulate metal and non-metal composite parts, there are examples using a roller disposed inside an oblique horizontal magnetron multi-arc ion coating machine to carry out the anti-corrosion coating process. However, the structure of the furnace is complex and has specific shape requirements for the coating samples. In addition, such an apparatus has not been in use in the field of vacuum coating Nd—Fe—B magnets.